In the past, dynamoelectric machines or electric motors of the resistance start induction run type, also known as resistance split phase motors, were utilized in a plurality of different applications and environments, such as for instance in furnaces, pumps, dehumidifiers, or the like and also in a hermetic environment for driving compressors of refrigerators or freezers or the like. While these past resistance split phase motors utilized a plurality of different winding circuits, a typical winding circuit included a main winding and a phase winding concurrently excited during a starting mode or energization of such a motor, and generally as the motor attained a predetermined running speed therefor, the phase winding was switched or otherwise electrically disassociated from the winding circuit by suitable means, such as for instance a current relay, a voltage relay or a centrifugal switch or the like.
These past resistance split phase motors generally utilized the resistance of the phase winding to achieve a desired current phase displacement between the current of the main winding and the current of the phase winding for effecting the starting mode of the motor. The necessary resistance to effect phase displacement was often achieved by providing both the main winding and the phase winding with a plurality of coils with each such coil comprising a predetermined number of forward conductor turns distributed in selected winding slots in a magnetic core of the motor, and in addition, an auxiliary winding having a plurality of conductor turns in a direction reverse from those of the phase winding was connected in circuit relation therewith. The magnetic field effected by the reverse wound turns as essentially cancelled by the magnetic field effected by corresponding effective forward wound turns in the phase winding.
In some of the winding circuits of the past resistance split phase motors, the above mentioned magnetic field cancelling effect was achieved by winding the phase winding in two parts and then connecting the two parts in the winding circuit so that the magnetic fields produced thereby were in a bucking relation. From the standpoint of terminology, subsequent discussion of reverse turns or reverse wound coils is intended to mean either turns or coils formed by winding in a direction opposite the forward wound coils of the phase winding, or turns or coils which are wound in the same direction but connected such that the direction of current flow therethrough is opposite the direction of current flow through the phase winding in a manner so as to produce bucking magnetic fields.
Because of the recent electrical energy shortage as well as the concomitant sharp increase in the cost of electrical energy, much more attention has been directed toward energy conservation, and increased efforts have been made to improve motor efficiencies with much of the effort being directed toward the design of capacitor run motors for applications in which the past resistance split phase motors have been used previously. Although capacitor run motors may effect an increase in operating efficiency, it is believed that one of the disadvantageous or undesirable features of such capacitor run motors is that the design and manufacture thereof may represent a considerable added expense in comparison with the past resistance split phase motors thereby limiting the applications where such capacitor run motors are economically feasible. For instance, it is believed that the economic feasibility of utilizing a capacitor run motor in lieu of a resistance split phase motor may be especially limited in situations where such capacitor run motor was designed to approach balanced operation in order to optimize operating efficiency. Furthermore, another disadvantageous or undesirable feature of the capacitor run motors is believed to be that at least some thereof may encounter problems resulting from low starting torque.
Efforts have been made in the past to broaden the range of applicability of capacitor run motors by developing starting arrangements to increase their starting torque. For example, externally connected resistors have been connected in series with the phase winding of the capacitor run motors, and a relay was utilized for disconnecting such externally mounted resistors during the running mode of the capacitor run motors.
As discussed previously, some resistance split phase motors were fabricated with a phase winding resistance which is achieved by associating a phase winding having forward conductor turns with an auxiliary winding having backward wound conductor turns, or by providing a two part phase winding wherein the respective parts were wound and disposed on the magnetic core such that their respective magnetic fields were in a bucking relation. However, the backward wound or disposed turns must either be removed from the winding circuit of the motor during the run condition or else a relatively large run capacitor must be utilized in order to improve motor operating efficiency.
One known approach for partially solving at least some of the previously discussed problems associated with the use of a phase winding having a reverse wound or disposed portion in a capacitor run motor is disclosed in U.S. Pat. No. 4,107,583, issued Aug. 15, 1978 to Jack A. Houtman which is incorporated herein by reference. This patent discloses, among other things, a connection arrangement wherein a reverse wound or disposed portion of a phase winding is disconnected during the running condition of the motor, thereby improving motor operating efficiency while obtaining a relatively high starting torque for the motor.
Another resistance split motor of the capacitor run variety is the subject of copending patent application Ser. No. 152,754 filed May 23, 1980 in the name of J. H. Johnson which is also incorporated herein by reference. In this motor, a phase winding and an auxiliary winding are disposed on a magnetic core of the motor, and a current relay reverses the manner in which the auxiliary winding is connected in series with the phase winding. During a starting mode or operation of the motor, the auxiliary winding is connected in series with the phase winding in such a manner that the magnetic field produced thereby is in bucking magnetic relation to the magnetic field produced by the phase winding. This increases the resistance of the combined windings and facilitates starting of the motor. During a running mode or operation of the motor, the connection of the auxiliary winding is reversed such that current flow therethrough establishes a magnetic field which is in an aiding or additive relation to the magnetic field produced by the phase winding. Thus, both the auxiliary and phase windings are utilized during the running mode of the motor to improve operating efficiency.
Although a reversible auxiliary winding has many salient features and manifestly is advantageous from the standpoint of efficient use of the winding because it functions in both the start and running modes, it is believed that a motor designer may often be faced with the necessity of compromising either starting or running torque, or both. For instance, if the auxiliary winding is chosen so that starting torque is optimized, then running torque may likely be somewhat less than optimum because the freedom of selection of the running auxiliary winding is no longer present. Conversely, if the auxiliary winding is chosen for optimum running torque, then starting torque may be compromised.